A liquid crystal display device and an EL (electroluminescence) display device which respectively have a liquid crystal element and a light-emitting element in each pixel are represented as a typical example of a display device. These display devices have display elements such as a liquid crystal element or an organic light-emitting element in each of the plurality of pixels formed over a substrate. A liquid crystal element and a light-emitting element have a pair of electrodes, and at least one of the pair of electrodes transmits visible light. For example, a light-emitting element has a structure in which a layer (hereinafter, referred to as an organic layer) including a light-emissive organic compound is sandwiched between a pair of electrodes and is designed so that at least one of the pair of electrodes transmits visible light.
As a typical material of an electrode which transmits visible light (hereinafter, referred to as a light-transmitting electrode), indium-tin-oxide (ITO) and indium-zinc-oxide (IZO) are represented. Japanese patent application publication No. 2008-84541 discloses an EL display device using an ITO film or IZO film formed by a sputtering method as a light-transmitting electrode